Which is the smallest exposure difference that can be detected and displayed by the imaging system?

• A. Spatial resolution
• B. Receptor exposure
• C. Subject contrast
• D. Contrast resolution

Answer: (D)

Contrast resolution is the imaging system’s ability to differentiate small differences in brightness on the image. The smallest exposure difference that can be detected and displayed depends on how many gray levels the system can represent, which comes from the receptor’s bit depth and the display’s capabilities, as well as the amount of noise in the image. More gray levels (higher bit depth) allow the system to separate finer differences in receptor exposure, so subtle variations in tissue attenuation appear as distinct shades rather than a single uniform tone. Spatial resolution, by contrast, concerns the ability to distinguish small details in space, not the subtlety of gray shades. Subject contrast refers to the inherent difference in attenuation within the object being imaged and sets the potential contrast, but doesn’t determine how finely those contrasts can be displayed. Receptor exposure affects overall brightness and signal level, not the smallest detectable difference in shades.